JP3714395B2 - Reinforcement method for the ground below existing structures - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a reinforcement method by improving the ground of the existing structure lower ground where there is a risk of ground subsidence or liquefaction during an earthquake.
[0002]
[Prior art]
In soft ground, due to the lack of sufficient bearing capacity for the foundation and problems of ground subsidence, when constructing a structure, it is necessary to improve the ground by injecting cement-based solidification material or chemicals, or to install drainage drains. It is necessary to take measures.
[0003]
In addition, loose sand ground with a relatively high groundwater level and saturation may cause liquefaction. Furthermore, from the example of the Great Hanshin-Awaji Earthquake, it has traditionally been considered that there is little risk of liquefaction during a major earthquake. It is known that liquefaction will occur even in the ground, and it is necessary to review it.
[0004]
For example, as shown in FIG. 4 , a caisson quay (gravity structure) as an existing structure 1 in a harbor is often constructed on a soft submarine ground. consisting landfill soil of the ground 3 and the back surface of the caisson just below consisting of ground 4 is liquefaction, which may suffer tremendous damage caused by the decrease of the shear resistance.
[0005]
In this case, the damage is particularly serious due to the decrease in shear resistance due to the liquefaction of the lower ground 3, and the restoration requires a great deal of cost and time. For the backside ground 4, various ground subsidence measures and liquefaction suppression measures that have been developed in the past, such as improving the ground or installing drainage drains to dissipate excess pore water pressure in the ground during an earthquake Can be applied.
[0006]
These are usually carried out by construction in the vertical direction or oblique direction, but it is difficult to apply the conventional countermeasure method as it is due to the existence of the structure 1 for the lower ground 3 of the existing structure 1. To construct the structure 1 through the structure 1, a large amount of money is required.
[0007]
In contrast, Japanese Unexamined Patent Publication No. 8 -120661 and JP 10-317883, do outer curved boring the ground surface of the structure, to form a borehole that traverses the lower existing structures, It is described that ground improvement and liquefaction measures can be taken using the borehole.
[0008]
[Problems to be solved by the invention]
According to the construction method described in JP-8 -120661 and JP 10-317883 discloses the above, instead of the construction of a conventional vertical or diagonal direction, substantially horizontal for under existing structures Since construction is carried out, ground improvement or drainage construction can be performed in such a way as to bypass the existing structure without passing through the existing structure.
[0009]
In addition, when boring holes are provided vertically or obliquely, the number of drilling holes must be increased and the extension distance per operation must be shortened, and the entire ground immediately under the existing structure is improved uniformly. It is difficult to economically arrange the drainage drains or densely arrange drainage drains.
[0010]
The present invention was developed under the circumstances as described above, and the ground under the existing structure was improved economically and efficiently, and the ground was liquefied during subsidence or earthquake. The purpose is to deter.
[0011]
[Means for Solving the Problems]
The ground reinforcement method for the lower ground of the existing structure according to claim 1 of the present application is that the ground is improved around the borehole using the borehole while boring the inside of the ground substantially horizontally. A portion is formed, and a ground improvement portion formed around such a boring hole is provided so as to surround the entire circumference of the ground to be reinforced when viewed in a vertical section .
[0012]
The diameter of the boring hole is preferably about 300 mm or less, and more preferably 150 mm or less, so that the cost for boring can be reduced. As for the ground improvement part formed around the borehole, it is assumed that the ground improvement part will be created in the range of 1 to 10 m in diameter by jetting cement-based solidified material or chemicals from the borehole at high pressure. are doing.
[0013]
Means for providing a borehole horizontally, to construct a vertical shaft on the outside of the existing structures, it is conceivable to perform boring in horizontal direction from the vertical shaft, JP-8 -120661 and JP 10 described above If free boring as described in Japanese Patent No. 317883 is performed from the ground surface, more economical construction is possible.
[0014]
If the layer thickness and the range of existing structures below ground is not so large, the entire existing structures below ground but the form is conceivable to surround the whole reinforcing target ground by ground improvement, partially depending on the circumstances It is conceivable to form a shape that surrounds as a ground to be reinforced , or to provide a plurality of such surrounding portions. The encircling shape is most commonly a square, but it may be encircling in a circle or an ellipse, and in that case, an arch effect of the reinforcing portion is also expected.
[0015]
The second aspect of the present invention is the reinforcement method of the lower ground of the existing structure according to the first aspect , wherein the same ground improvement portion is further divided so as to partition the inside of the ground improvement portion provided so as to surround the entire circumference of the target ground. Is provided in a plate shape. When the layer thickness or width is large, the unimproved portion can be constrained into small portions by reinforcing the ground improvement portion so as to partition the inside, and the overall reinforcing effect can be enhanced.
[0016]
Claim 3, in claim 2, wherein said ground improvement portion dividing the inner characterized in that it is a swash wall. For example, when it is surrounded by a square when viewed in a vertical cross section, the slant wall part functions as a brace by reinforcing the inside with a slant wall composed of a ground improvement part, and the strength of the ground improvement body as a whole Can be increased.
[0017]
According to a fourth aspect of the present invention, in the reinforcement method for the lower ground of the existing structure according to the first, second, or third aspect , the ground also extends in a direction substantially orthogonal to the ground improvement portion provided so as to surround the entire circumference of the target ground. A similar ground improvement portion is provided in the form of a vertical wall in the form of partitioning the improvement portion in the longitudinal direction.
[0018]
The vertical wall-shaped ground improvement part that is orthogonal to the longitudinal direction also acts as a seismic wall against the horizontal force during an earthquake. As a countermeasure for ground subsidence, it is effective to form a ground improvement portion in a three-dimensional mesh shape in combination with claims 2 and 3 .
[0019]
A fifth aspect of the present invention relates to the reinforcing method for the lower ground of the existing structure according to any one of the first to fourth aspects, wherein the boring hole is provided with a plurality of nozzles for injecting grout material in a predetermined section of the tip, And a step of digging a predetermined section with the packer contracted, and then expanding the packer to the hole wall of the boring hole. The ground improvement portion is formed by repeating a step of improving the ground around the borehole by ejecting a grout material from the nozzle at a high pressure in the state of being in close contact.
[0020]
According to the fifth aspect of the present invention, the expansion and contraction of the packer and the ejection of the grout material such as cement milk from the nozzle are interlocked, so that the boring and the grout process can be integrated, and sufficient grout penetration injection can be performed at a limited position. In addition, it can be expected to improve economy and workability.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 schematically shows an embodiment of the invention according to claims 1 to 3 of the present application, in which a boring hole is formed by boring from a ground surface at a distance from a soft ground 3 below an existing structure 1. 6 is drilled, and the ground improvement portion 7 is formed around the bored hole 6 by using the bored hole 6.
[0022]
Such a ground improvement portion 7 is provided in a square shape so as to surround the target ground (in the figure, 7A is a square portion), and the ground improvement portion 7 is provided obliquely in the form of a plate on the inside thereof, thereby the slant wall portion 7B. Is forming. The rectangular portion 7A extends in the longitudinal direction of the structure 1 such as a caisson quay, reinforces the ground below the structure 1, and further provides a slant wall portion 7B on the inner side thereof. On the other hand, this portion can function in a truss structure.
[0023]
FIG. 2 conceptually shows the form of the ground improvement portion in the invention according to claim 4 of the present application, and is orthogonal to the rectangular portion 7A provided so as to surround the ground improvement portion 7 around the target ground. A ground improvement portion using a bored hole is provided in a vertical wall shape from the direction, and the rectangular portion 7A is partitioned in the longitudinal direction by the vertical wall-shaped portion 7C.
[0024]
This vertical wall-shaped portion 7C can function as a seismic wall against the horizontal force during an earthquake in addition to the function as a countermeasure for ground subsidence. FIG. 3 shows an example of the construction procedure of ground improvement by boring and grouting from the boring hole 6 in the invention according to claim 5 of the present application in which the boring and grouting processes are unified, and the work is performed according to the following procedure. It can be carried out.
[0025]
(1) by self-standing boring and drilling to the lower ground to be liquefaction measures (see Figure 3 (a)).
[0026]
(2) The packer 12 made of a rubber bag or the like provided behind the nozzle at the tip of the rod 11 of the boring device is inflated, and grouting (cement milk, etc.) is sprayed from the nozzle at the tip at a high pressure in the radial direction. Then, improve the ground (see Fig. 3 (b)).
[0027]
(3) Shrink the packer 12 and drill the next section (see Fig. 3 (c)).
[0028]
(4) Expand the packer 12 and, like (2), inject the grout from the nozzle at high pressure to improve the ground in this section (see Fig. 3 (d)).
[0029]
(5) Thereafter, drilling and grouting are repeated to create a ground improvement body for a predetermined section, and then filling the hole while pulling out the rod 11 (see FIG. 3 (e)).
[0030]
Thus, one ground improvement portion 7 is created.
[0031]
【The invention's effect】
(1) In the invention according to claims 1 to 3 of the present application, by providing a ground improvement portion using a boring hole so as to surround the target ground in a vertical section, including the restraining effect of the unimproved portion on the inside, The reinforcement effect of the ground can be enhanced by reinforcing the target ground and further forming a plate-like or slanted wall-like ground improvement body that partitions the inside as necessary.
[0032]
(2) In this way, it will be restrained from the surroundings with a ground improvement part that secures strength, economically and efficiently with less boring, improving the ground under existing structures, subsidence and liquefaction of the ground Ru can suppress.
[0033]
(3) In the invention according to claim 4 of the present application, in contrast to the inventions according to claims 1 to 3 , the reinforcing effect can be further enhanced by partitioning the inner side with a vertical wall-shaped portion substantially perpendicular to the longitudinal direction. it can.
[0034]
(4) In the invention according to claim 5 , the expansion and contraction of the packer and the ejection of the grout material such as cement milk from the nozzle are interlocked to unify the boring and grout processes, and further improve the economy and workability. Improvements can be made.
[Brief description of the drawings]
FIG. 1 is a vertical perspective view showing an embodiment in which the invention according to claims 1 to 3 of the present application is applied to a ground below a caisson quay as an existing structure.
FIG. 2 conceptually shows the form of a ground improvement portion in an invention according to claim 4 of the present application, wherein (a) is a sectional perspective view and (b) is a plan view.
FIG. 3 is a cross-sectional view showing a construction procedure for ground improvement by grouting from a boring and a boring hole in the invention according to claim 5 of the present application;
FIG. 4 is a vertical sectional view conceptually showing a damage situation of a caisson quay as an existing structure when liquefaction measures are not taken.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Existing structure, 2 ... Foundation rubble, 3 ... Lower ground (replacement sand), 4 ... Back ground (landfill), 5 ... Clay layer, 6 ... Boring hole, 7 ... Ground improvement part, 7A ... Square part, 7B: Oblique wall portion, 7C: Vertical wall portion, 11 ... Rod, 12 ... Packer

Claims (5)

While the ground below the existing structure is drilled almost horizontally in the ground, a ground improvement portion is created around the borehole using the borehole, and the ground formed around the borehole. A method for reinforcing the lower ground of an existing structure, wherein the improved portion is provided so as to surround the entire circumference of the ground to be reinforced when viewed in a vertical section. So as to partition the interior of the ground improvement portion provided so as to surround the entire circumference of the ground of interest, existing structures below ground according to claim 1, wherein the providing a further similar ground improvement moiety to the plate-like Reinforcement construction method. The method for reinforcing the ground below the existing structure according to claim 2, wherein the ground improvement portion that partitions the inside is a slant wall. A similar ground improvement portion is provided in the form of a vertical wall in the form of partitioning the ground improvement portion in the longitudinal direction in a direction substantially perpendicular to the ground improvement portion provided so as to surround the entire circumference of the target ground. The reinforcing method for the ground below the existing structure according to claim 1, 2, or 3 . The construction of the boring hole is performed by a boring device having a plurality of grout material injection nozzles in a predetermined section at the tip, and having a packer that is radially expandable behind the section provided with the plurality of nozzles, A step of digging a predetermined section in a state where the packer is contracted, and then, in a state where the packer is inflated and in close contact with the hole wall of the boring hole, a grout material is ejected from the nozzle at a high pressure, and the ground around the boring hole The method for reinforcing the ground below the existing structure according to any one of claims 1 to 4 , wherein the ground improvement portion is created by repeating the step of performing improvement a required number of times.

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